Note: Descriptions are shown in the official language in which they were submitted.
CA 02455802 2004-O1-23
A ROCK STABILIZING APPARATUS
BACK GROUND OF THE INVENTION
Field of the Invention
This invention relates to a rock stabilizing apparatus for anchoring unstable
rock
formations in underground mines and more particularly relates to an apparatus
using a
tension member that is embedded into a hardenable adhesion material for
creating
stabilizing forces within an unstable rock formation.
Background of the Invention
In underground mines it is important to secure the roof and walls of a tunnel
against
collapse of unstable rock formations that will hang from stable rock
formations. Such
situations may be caused by having to tunnel through naturally fractured rock
formations
or by blasting operations within the mine. Scaling the roof and walls of a
newly formed
tunnel is necessary to remove loose rock that could easily collapse. Scaling
is a process
whereby a miner uses a long pole to pry and remove loose rock, called scale,
from the
roof and walls of the tunnel. After removing the scale it is necessary to
anchor the walls
and roof of the tunnel to more stable rock formations. This is accomplished
through the
use of devices that are generally called rock bolts. Holes are: drilled into
the walls and
roof of the tunnel a sufficient distance to penetrate the unstable formations
surrounding
the roof and walls of the tunnel and enter stable formations. Rock bolts of
adequate
~~ ~~~~~
CA 02455802 2004-O1-23
length are then inserted into the holes. The inserted end of the rock bolt is
anchored to
the stable rock formation using mechanical expansion clamps or hardenable
adhesion
material. The end of the rock bolt protruding from the hole is generally
threaded. A nut
and anchor plate is often used to apply a stabilizing compressive force to the
rock
formation and tension the rock bolt supporting the roof and wall loads. Steel
netting may
be strung across the roof and walls from plurality of rock bolts for further
security. As
well, concrete is often applied to the surfaces of the tunnel providing even
more strength
to the tunnel. Where adhesion material is used to anchor the rock bolt to the
stable rock
formation the rock bolt can be used to rotate and mix the adhesion material so
that it will
cure and bind the bolt to the walls of the borehole.
A number of roof bolts and anchoring systems using harden;~ble materials have
been
proposed for use in mining applications. One example is found in United States
Patent
4,904,122 "Anchoring Device, Such As A Rock Anchor" issued to Herbst and
Schnitzler
in 1990. This device is not well suited to applications where; the reinforcing
rod is used
to mix adhesion materials during curing because there is disclosed no way to
rotate the
rod within the hole. Another example is found in United States Patent
4,051,683
"Method and Apparatus For Supporting A Mine Roof' issued to Koval in 1977.
This
system has a number of disadvantages. It relies upon a plurality of parts
making it
difficult to use in underground mining operations. It relies upon on a
relatively complex
coupling device that that will be expensive to manufacture and therefore adds
expense to
the cost of the overall system. The reliance upon a coupling between the
bolting rod and
the reinforcing rod creates a weak link that may fail during rotation
necessitating the
2
CA 02455802 2004-O1-23
entire system and adhesion material to be removed from the hole. A similar
system is
found in United States Patent 5,785,463 "Combination Cable Bolt System" issued
to
Eaton et al in 1998 having similar deficiencies relating to complexity,
expense and
inherent weaknesses caused by coupling mechanisms
Therefore there is a continued need for an apparatus for anchoring unstable
rock
formations in underground mines using a tension member with adhesion materials
that is
simple and inexpensive to manufacture and use and does not rely upon coupling
mechanisms with their inherent weaknesses.
OBJECTS OF THE INVENTION
It is an object of the present invention to overcome the deficiencies in the
prior art.
It is a further object of the invention to provide a rock stabilizing
apparatus for anchoring
unstable rock formations in underground mines.
Yet another object of the present invention is to provide a rock stabilizing
apparatus for
anchoring unstable rock formations adapted for applications where adhesion
materials are
used to fix the reinforcing member within the borehole.
Still another object of the invention is to provide a rock stabilizing
apparatus for
anchoring unstable rock formations in underground mines using a tensionable
member
3
CA 02455802 2004-O1-23
and adhesion materials that is easy and inexpensive to and manufacture; does
not rely
upon a plurality of dependent parts; and, does not rely upon a coupling
device.
SUMMARY OF THE INVENTION
The objects of the present invention are satisfied through the provision of a
rock
stabilizing apparatus for anchoring unstable rock formations adapted for use
with
adhesion material. The apparatus comprises an elongated re;inforciiig member
having a
threaded portion at a bottom end; and, a top end adapted to be embedded
permanently
within a hardenable adhesion material within the drilled hole. The threaded
bottom
portion and the top end are at opposite ends of the same member. The
reinforcing end is
inserted into a drilled hole through the unstable rock formation into stable
rock. The
drilled hole is sufficiently deep so that when the member is entirely inserted
into the
drilled hole the threaded end is partially inserted into the drilled hole.
There is at least
one bearing plate member retained on the threaded bolt portion of the
reinforcing
member. The threaded portion has a top end and a bottom end, and can be
rotated
through the centre of the plate. The plate can be advanced so that it abuts
against the rock
face for transmitting compressive forces to the rock face. There is at least
one nut
threadably advanceable over the threaded portion. The nut acts to advance the
bearing
plate to the rock face and applies a tensioning force into the reinforcing
member when it
is tightened against the bearing plate. A shearing element is provided within
the nut that
shearably fixes the nut to a predetermined and variable position on the
threaded portion
of the reinforcing member. The nut has a first temporary prey torquem~
operating position
wherein it is fixed to the member-threaded portion at its bottom end by the
sheaxing
4
CA 02455802 2004-O1-23
element thus permitting the nut and member to be rotated a~: one. The first
temporary
pre-torque operation position is adopted when it is necessary to mix adhesion
material
within the borehole for curing. The nut has a second post-torque,~X permanent
operation
position that is adopted once the shearing element has sheared at torque~,~
and the nut is
free to advance along the threaded portion of the reinforcing member. This
second post-
torque operating position is adopted when it is necessary to abut the bearing
plate
against the rock formation and then further torque the nut to torque,r,aX thus
adding
compressive forces to the rock formation through the bearing plate and also
adding
tensile forces to the reinforcing member anchored within the drilled hole. The
shearing
element is adapted to shear at torquesh~r when a predetermined amount of
torque is
applied to the nut. Torquesh~r occurs at a predeterminable torque that is made
dependent
upon the curing properties of the adhesion material. The breakage of the
shearing
element at torques~t will not damage the threads on the member. Additionally,
the
remnants of the shearing element, once sheared, are retained within their
respective bores
to eliminate safety hazards that may result from energized pieces of the
shearing element
acting as projectiles.
A method is provided for using a rock stabilizing apparatus in underground
mining
operations. A hole is drilled through unstable rock strata a substantial
distance into stable
rock strata. The reinforcing member is prepared by threading at least one nut
onto the
threaded end of the reinforcing member and then fixing the nut to the threaded
portion of
the member using at least one shearing element. Typically, 'the members will
arrive on
site with the nut akeady threaded and fixed to the reinforcing member. The
member will
5
CA 02455802 2004-O1-23
also be of a predetermined length and width adapted to fit the drilled hole.
The shearing
element will also have a torquesh~,. that is predetermined to suit the size
and strength of
the member and the properties of the adhesion material. At least one bearing
plate is then
placed on the unthreaded end of the member and moved to the threaded end. The
member is inserted into the drilled hole and the hardenable adhesion material
is inserted
into the annulus between the member and the drilled hole walls. A rotational
movement
is imparted to the member through the nut by a rotating device in order to
thoroughly mix
the adhesion materials elements and fill the annulus between the reinforcing
member and
the walls of the drilled hole. Once the adhesion material stiffens, additional
torque will
1U have to be applied to the nut until the shearing element reaches its
torques~~r . Once the
shearing element fails, the nut will advance towards the rock face along the
threads
forcing the bearing plate into an abutting relationship against the rock face.
A
predetermined amount of torque~X can then be applied to the nut thereby
tensioning the
reinforcing bar by a desired amount.
Further objects and advantages of this invention will become apparent from a
consideration of the following drawings, detailed description and claims.
6
CA 02455802 2004-O1-23
BRIEF DESCRIPTION OF THE DRAWINGS
Figure I is a partial sectional side view of a rock stabilizing apparatus for
anchoring
unstable rock formations in an underground mine according to a preferred
embodiment of
the present invention showing the nut in its first operating position.
S
Figure 2 is a sectional side view of the nut of a preferred embodiment of the
present
invention.
Figure 3 is a top view of the nut of a preferred embodiment of the invention.
Figure 4 is a side partial sectional view of a rock stabilizing apparatus for
anchoring
unstable rock formations in an underground mine according to a preferred
embodiment of
the invention showing the nut in its second operating position.
1 S Figure S is a partial sectional side view of the nut and shearing element
used a preferred
embodiment of the invention.
Figure 6 is a front view of the nut showing the shearing element
DESCRIPTION OF THE INVENTION
Referring to Figure I there is shown a rock stabilizing apparatus for
anchoring unstable
rock formations (12) to stable rock formations (I4) in mining operations of a
preferred
embodiment of the invention generally designated as (10). 7Che apparatus is
shown in its
7
CA 02455802 2004-11-29
CA2455802 Replacement Sheet
pre-torque", and pre-torque~,~ states. The apparatus is adapted to be inserted
into a pre-
drilled hole (16) that extends through the unstable portion (12) to a stable
portion (14) of
the rock formation as might be found in the roof or wall of a mine tunnel. The
apparatus
comprises a tensionable member (18). In a preferred embodiment of the
invention the
member is a reinforcing member generally tubular in shape having a top ribbed
portion
(100) and a bottom threaded portion (101). In alternative embodiments of the
invention
the reinforcing member may comprise one of a steel bar, a cone bolt, a
standard rock bolt,
or a reinforcing cable. The portion inserted into the drilled hole may be
smooth or
textured to promote adhesion to the adhesion material. As shown in Figure 1,
the
diameter of the member (18) is less than the diameter of the drilled hole
{16). This forms
an annulus (103) around the member (18). The annulus is filled with a suitable
hardenable adhesion material (102) such as a polyester resin. Using resin to
exemplify a
preferred embodiment, the resin may be inserted into the drilled hole prior to
insertion of
the member as binary packages so that when the rod is inserted into the
drilled hole the
packages are ruptured and their contents mix and cure into a hardened resin.
Alternatively, the resin may be formulated in such a way that it can be pumped
onto the
annulus after the member is inserted and mixed and cured by rotation (105) of
the
member in the drilled hole as further described herein. The ribbed portion
(100)
facilitates the fixing of the adhesion material to the member. The adhesion
material (102)
can also be a cementatious material depending upon the nature of the
installation and the
type of rock. The adhesion material (102) operatively connects the member (18)
to the
wall (104) of drilled hole (16) permitting the transfer of forces between the
member and
the rock formation through the adhesion material. As shown in this preferred
CA 02455802 2004-O1-23
embodiment of the invention, the entire ribbed portion (100;) of the member
and a small
threaded portion (108) is inserted into the drilled hole (16). This permits
bearing plate
(106) to be placed in a tight abutting relationship with the face of the rock
formation
(110) as shown in Figure 4. Bearing plate (106) is adapted to move freely
along the
length of the threaded portion (i01) of the member so that as nut (112) is
advanced along
threaded portion (101), the bearing plate can be forced into an abutting
relationship with
the rock face and compressive forces applied to the rock formation. It is
understood that
multiple bearing plates and washers can be installed between nut (112) and the
rock face
( 110) as required. Nut ( 112) is preferably a square nut because a square nut
can be driven
by existing rock bolt installing apparatus. The corners of the square nut are
also more
resistive to shearing forces generated when Iarge amounts o:Ptorque are
applied to the nut
such as during tensioning of the member. However, where appropriate, other
conventional polygonal nut shapes can be used. A single shearing element (50)
is shown
placed within the second bore (38) as more fully described below.
Referring to Figure 2 there is illustrated in partial sectional side view a
square nut (112)
used in a preferred embodiment of the present invention. The nut ( 112) is
threadably
received onto the threaded portion (101) ofthe member (18). Bearing plate
(106) is
illustrated abutting against nut (112). In alternative embodiments of the
invention there
may be more than one nut installed on the member. A single shearing element
(50) is
shown placed within the second bore (38) as more fully described below.
9
CA 02455802 2004-O1-23
Referring to Figure 3, there is illustrated in sectional top view the nut
(112) in a preferred
embodiment of the invention having a square body portion (30). A first
threaded bore
(32) extends axially through the body (30) of the nut. The outside diameter of
the thread
is represented by line (34) and the inside diameter of the thread is
represented by line
(36). The nut also comprises a second bore (38) positioned intermediate of the
length of
the nut and extending transversely through the top portion of the nut. In
other
embodiments of the invention there may be more than one second bore positioned
intermediate of the length of the nut. Referring back to Fign:~re 2, the
second bore (38) is
located in the top portion of the nut (I 12). It is understood that nut (112)
is sufficiently
dimensioned so that the placement of second bore (38) or more than one second
bore
within the body of the nut does not degrade is strength or its ability to
tensionably hold
the bearing plate against the rock face. Figure 4 illustrates that the
apparatus further
comprises an additional third bore (40) intermediate of the threaded portion
of the
reinforcing member (101). As shown in Figure 2, bore (38) in the nut and bore
(40) in
the threaded portion of the member are axially aligned to pe:rnlit the
insertion of a
shearing element (50) that fixes nut (112) to threaded portion (101) and
prevents
independent movement between them. It is understood that the third bore (40)
may be
located anywhere along the length of the threaded portion ofthe member (101)
to suit
installation requirements. It is further understood that when more than one
second bore is
placed in the nut there will be corresponded co-axial third bores in the
member threaded
portion.
CA 02455802 2004-O1-23
Referring to Figure 5 there is shown in greater detail and in sectional side
view the single
shearing element (50) of a preferred embodiment of the invention. Nut (112) is
shown
having body (30) and first bore (32) extending axially along the body of the
nut. Also
shown is second bore (38) extending transversely through the top portion of
the nut.
Within second bore (38) is inserted shearing element (50) that fixes nut (112)
to the
threaded member (101). Shearing element (50) fits within the length of the
second bore
(38) and does not extend beyond the outer edges of the second bore.
Referring to Figure 6 there is shown in front elevation view, nut (112) and
second bore
(38) with shearing element (50) inserted in the second bore. Shearing element
(50) forms
a member having compression gap (51). Shearing element (SO) is manufactured
from
material having significant tensile strength, such as spring steel. In its
first unbiased
state, shearing element has a diameter that is slightly larger khan the
diameter of the
aligned second and third bores (38 and 40). The shape and compressibility of
shearing
element (50) permits the shearing element to adopt a second fully biased
configuration so
that the sides of the compression gap (51) are brought together. The resulting
shape has a
diameter slightly smaller than the diameter of the aligned second and third
bores (38 and
40) so that the shearing element slides easily into the second and third bores
while a
compressive force maintained on the shearing element. Once the shearing
element is
placed within the aligned second and third bores the compressive force is
released and the
shearing element is permitted to expand into a third partially biased position
within the
diameter of the aligned second and third bores. Since the diameter of the
second and
third bores is less than the diameter of the shearing element in its unbiased
state, a
11
s.... a y ._ _ ~~.,-~~~~:. , ~~.~.,~~:,~-~..~~.-~~~~ ~.m-~~.~~..~;:~,,~
.~.~W._ _.~.~.~-~~...M~~~..~.m~~~.~ .~~._-~~
CA 02455802 2004-O1-23
significant biasing force is generated by the shearing element against the
inside walls of
the second and third bores (38). This biasing force has two advantages. The
first is that
the shearing element acts like a compression clip. It may be: easily inserted
into the
aligned bores (38) and (40) during assembly of the apparatus by compressing
the element
beyond its resting state and inserting it into the aligned bores. Then once
the shearing
element is released, it expands to exert significant biasing farces against
the walls of the
bores. Therefore, prior to shearing the shearing element will remain
stationary within the
bores and will not drop out and be lost or be displaced by agitation. The
second
advantage occurs after the shearing element has been sheared. Since each
residual
portion of the sheared element continues to exert a biasing force it will
remain with its
respective bore a$er shearing. This prevents pieces of the shearing element
becoming
jammed in the threads and damaging the threads and prevents the pieces of the
shearing
elements from causing a safety hazard to nearby workers. Shearing element (50)
is
manufactured from a suitable tensile material. Shearing element has a length
slightly less
than the length of the second bore (38) so that no portion of the shearing
element extends
beyond the body of the nut. The circumference of the shearing element is
slightly less
than the circumference of the bores (38 and 40) thus permitting biasing forces
(52) to act
upon the inside walls of the bores. Other shearing elements can be used such
as solid pin
members, cotter pins, bolts and nails.
Referring back to Figures 1 and 4, the nut (112) has a first pre-torque
temporary
operating position as illustrated in Figure 1 and a second post-torquem~
permanent
operating position as illustrated in Figure 4. In Figure 1, the nut (112) is
temporarily
12
r
CA 02455802 2004-O1-23
fixed to the threaded portion of the member (101) by a single shearing element
(50)
located within axially aligned transverse bore (38) and bore (40) in the
threaded portion
ofthe member (not shown). The nut (112) and the member (101) are rotatable
together
as a single unit. Nut (112) will be coupled to an at least one nut rotation
device (47) to
impart a rotation (145) to the nut and member. Therefore, with the nut fixed
in its first
temporary operating position by shearing element (50), the ribbed portion of
the member
(100) is inserted into the drilled hole (16) with the adhesion material (102)
placed in the
drilled hole prior to insertion of the member or after insertion of the
member. Sufficient
torque is applied to nut (112) so as to rotate the ribbed portion (100) thus
agitating the
adhesion material (102) so that it mixes and fills annulus (103). The nut and
member
may be rotated clockwise or counter clockwise as desired. As the adhesion
material cures
it becomes stiffer and more difficult to rotate the member within the
material. Therefore,
additional torque must be applied to the nut. At a predetermined amount of
torquesn~,.
applied to the nut selected to coincide with the cured stiffness of the
adhesion material
used, shearing element will shear permitting nut (112) to rotate freely along
the threaded
portion of the member (101). Since the remnants of the shearing element do not
interfere
with the threads there is negligible residual torque on the nut as it advances
towards the
rock face. The nut and bearing plate (106) are then advanced along the length
ofthe
member so that the shearing plate comes into abutting contact with the rock
face (110).
The nut (112) now assumes its second post-torquem~ permanent operating
position as
shown Figure 4. In its second permanent operating position" nut (112) is
abutted against
bearing plate (106) that is in turn abutting against the rock favce (110).
Adhesion material
(102) fills annulus (103) and has cured to a desired hardness so that
stabilizing forces can
13
CA 02455802 2004-O1-23
be transmitted between the rock formation and the ribbed portion (100). In
this
configuration, a predetermined amount of torquemaX is added to nut ( 112) to
tension the
member. The amount of torque",aX is dependent upon the length of the member,
the type
of adhesion material used and the application of the system. As it is torqued,
nut ( 112)
forces plate (106) against rock face (110), which in turn exerts compressive
forces (42)
between the unstable rock ( 12) and the stable rock ( 14). The torquing of nut
( 112) also
creates tension forces (44) in the ribbed portion (100) now anchored to the
stable rock
(14) by the adhesion material (102) further adding stability to the rock
formation.
After the shearing element (50) has sheared, remnants remain within their
respective
bores to prevent safety hazards to the workers and damage to the threads
(101).
Therefore, additional items may be added to the threaded portion (101) as
desired. For
example, a second square nut may be placed on the bar (101) and torqued behind
the first
nut ( 112).
Although the description above contains many specifications, these should not
be
construed as limiting the scope of the invention but as merely providing
illustrations of
some of the presently preferred embodiments of this invention. Thus the scope
of the
invention should be determined by the appended claims and their legal
equivalents rather
than by the examples given.
14
